Thanks for your help Walkir. Gradient notebooks on Paperspace are not the same as machine instances on Paperspace. I talked to their support, and they said this:
"Currently you cannot SSH into notebooks, only jobs. If you want to run an autoshutdown script I would advise putting it in your notebook and run that code.
As for CLI user/password that should be your Paperspace credentials."
So, I’ll try the auto-shutdown that way now.